Core: Ramp down MainWindow in it's ICore::pimpl function

Change-Id: I7c4934248ea4794f7d4eb95f98d19994b56fa0f1
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/coreplugin/coreplugin.cpp

@@ -319,7 +319,7 @@ QObject *CorePlugin::remoteCommand(const QStringList & /* options */,
         return nullptr;
     }
     const FilePaths filePaths = Utils::transform(args, FilePath::fromUserInput);
-    IDocument *res = MainWindow::openFiles(
+    IDocument *res = ICore::openFiles(
                 filePaths,
                 ICore::OpenFilesFlags(ICore::SwitchMode | ICore::CanContainLineAndColumnNumbers | ICore::SwitchSplitIfAlreadyVisible),
                 FilePath::fromString(workingDirectory));